Gas turbine components are subjected to thermally, mechanically, and chemically hostile environments. For example, in the compressor portion of a gas turbine, atmospheric air is compressed, for example, to 10-25 times atmospheric pressure, and adiabatically heated, for example, to 800°-1250° F. (427° C.-677° C.), in the process. This heated and compressed air is directed into a combustor, where it is mixed with fuel. The fuel is ignited, and the combustion process heats the gases to very high temperatures, for example, in excess of 3000° F. (1650° C.). These hot gases pass through the turbine, where airfoils fixed to rotating turbine disks extract energy to drive the fan and compressor of the turbine, and the exhaust system, where the gases provide sufficient energy to rotate a generator rotor to produce electricity. To retain sufficient strength and avoid oxidation/corrosion damage at high temperatures, coatings have been applied to the surface of metallic components and cooling schemes have been implemented so that the components function well and meet the designed life.
To improve the efficiency of operation of gas turbines, combustion temperatures have been consistently raised. With the higher temperatures, the materials used to make the component become too weak to accomplish their functions or even start to melt. Traditionally, air is used for temperature control. This requires cooling holes to be drilled through the critical locations in a coated component. A typical high temperature gas turbine blade or vane may contain hundreds of small cooling holes on the airfoil surfaces to cool metal components, for example, there can be over 700 cooling holes in a stage-1 nozzle of a typical advanced gas turbine, which is usually coated with a thermal barrier coating (TBC).
A significant challenge in the manufacture or repair of cooled turbine components is ensuring the flow of cooling air is correct to provide the proper amount of cooling. If the flow is too low, there is potential for backflow margin and potential for the component to become too hot, resulting in potential damage to the component. If the flow is too high, there are turbine performance concerns. If a component flow is too low, holes can be reopened or enlarged to allow for additional flow. However, when a part flows too high, known methods for modifying flow require that the component be stripped of its TBC coating, recoated with a new TBC coating and re-clear the cooling holes in an attempt to restore flow to the desired values. This is an expensive and time consuming option and has no guarantee of fixing the issue.
A method for modifying the flow through apertures, such as cooling holes, that does not suffer from one or more of the above drawbacks would be desirable in the art.
Intended advantages of the disclosed systems and/or methods satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.